The present invention relates generally to pumping arrangements, and more particularly to pumping arrangements with stationary pistons and movable cylinders.
There are already known various constructions of pumping arrangements with stationary pistons and movable cylinders. Examples of such pumping arrangements can be found, for instance, in U.S. Pat. Nos. 661,938 and 3,236,190. However, in the known constructions, the cylinders reciprocate along a straight line. This makes the construction of the respective pumping arrangement rather complex, with substantial reciprocating masses. Therefore, such known constructions are not suited for use as energy-efficient small pumps.
On the other hand, there are also already known, for instance, from U.S. Pat. Nos. 3,961,868, 3,961,869, 4,028,015 and 4,275,999, mini-compressors with stationary cylinders and movable pistons, the respective piston being driven by an eccentric element mounted on the output shaft of an electric motor into reciprocation and angular displacement or wobbling in the respective cylinder. However, in these known constructions, both the cylinder and the piston are received in the interior of a crankcase, at a location outside the flow path of cooling air through the interior of the electric motor and the crankcase. Therefore, the cylinder and piston are very ineffectively cooled, if at all, in such known constructions. This brings about the disadvantage that the sealing element, such as a cup-shaped seal that is mounted on the piston and sealingly contacts the cylinder, is subject to a high degree of wear, since the wear rate is proportional to the operating temperature of the seal and thus of the cylinder and the piston. Moreover, these known constructions are hardly amenable to field servicing, since the entire assembly must be disassembled before access can be had to the parts which need periodic servicing or replacement, such as the sealing element.